Eastern, Western, and Venezuelan Encephalitis or “sleeping sickness” are viral infections of the brain and spinal cord in horses that are transmitted by mosquitoes. Eastern Equine Encephalitis or “Triple E” is seen mostly in the eastern half of the United States, with the majority of the 116 cases reported in 2016 originating from Florida, Wisconsin, South Carolina, and Louisiana. EEE is the most serious of the three diseases, with a fatality rate of nearly 90%. As the name suggests, Western Equine Encephalitis or WEE occurs mostly in states west of the Mississippi and its mortality rate is much lower, near 50%. Venezuelan Equine Encephalitis (VEE) primarily strikes in Central and South America; a case has not been reported in the U.S. in 40 years.
Like many infections, Eastern and Western sleeping sickness initially cause listlessness, lack of appetite, and fever, but in less than a day a horse with either disease will show neurologic signs such as:
Signs quickly progress to partial or complete paralysis, an inability to rise, convulsions, and death in some cases.
Because there are several diseases and conditions that overlap in their clinical signs with equine encephalitis such as West Nile Virus (WNV), EPM, Equine Herpesvirus-1 (EHV-1), and others, it is important for a veterinarian to obtain an accurate diagnosis in order to provide appropriate treatment and prevent spread if contagious. The veterinarian will take into consideration clinical signs, geographic location and season, and vaccination history, along with diagnostics such as routine bloodwork, spinal tap, nasal swabs, and specific antibody tests to rule in or out each possible cause. Note that some tests can be performed “in-house” or in the veterinary clinic while others must be sent away to a diagnostic laboratory with special equipment.
Because eastern and western encephalitis are caused by a virus, treatment primarily consists of supportive care, which means keeping the horse comfortable and hydrated while the disease runs its course. Intravenous fluids and corticosteroids are commonly given, as well as other medications and care as is necessary in each particular situation. Until diagnosis is confirmed and there is the possibility that signs could be due to another disease or condition such as EPM, specific treatment with additional medications may be administered.
SmartPak strongly encourages you to consult your veterinarian regarding specific questions about your horse's health. This information is not intended to diagnose or treat any disease, and is purely educational.